FAQ 7.15 How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?

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7.15: How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?

    You need to pass references to these objects. See "Pass by Reference" in
    perlsub for this particular question, and perlref for information on

    Passing Variables and Functions
        Regular variables and functions are quite easy to pass: just pass in
        a reference to an existing or anonymous variable or function:

                func( $some_scalar );

                func( \@some_array  );
                func( [ 1 .. 10 ]   );

                func( \%some_hash   );
                func( { this => 10, that => 20 }   );

                func( \&some_func   );
                func( sub { $_[0] ** $_[1] }   );

    Passing Filehandles
        As of Perl 5.6, you can represent filehandles with scalar variables
        which you treat as any other scalar.

                open my $fh, $filename or die "Cannot open $filename! $!";
                func( $fh );

                sub func {
                        my $passed_fh = shift;

                        my $line = <$passed_fh>;

        Before Perl 5.6, you had to use the *FH or "\*FH" notations. These
        are "typeglobs"--see "Typeglobs and Filehandles" in perldata and
        especially "Pass by Reference" in perlsub for more information.

    Passing Regexes
        Here's an example of how to pass in a string and a regular
        expression for it to match against. You construct the pattern with
        the "qr//" operator:

                sub compare($$) {
                        my ($val1, $regex) = @_;
                        my $retval = $val1 =~ /$regex/;
                return $retval;
                $match = compare("old McDonald", qr/d.*D/i);

    Passing Methods
        To pass an object method into a subroutine, you can do this:

                call_a_lot(10, $some_obj, "methname")
                sub call_a_lot {
                        my ($count, $widget, $trick) = @_;
                        for (my $i = 0; $i < $count; $i++) {

        Or, you can use a closure to bundle up the object, its method call,
        and arguments:

                my $whatnot =  sub { $some_obj->obfuscate(@args) };
                sub func {
                        my $code = shift;

        You could also investigate the can() method in the UNIVERSAL class
        (part of the standard perl distribution).


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